High melting polyolefin filamentary materials



April 9, 1968 H. D. NOETHER ET AL 3,377,329

HIGH MELTING POLYOLEFIN FILAMENTARY MATERIALS Original Filed Nov. 21. 1960 ELONG'ATION,

United States Patent 3,377,329 HIGH MELTING POLYOLEFIN F-ILAMENTARY MATERIALS Herman Dietrich Noether, 'Millburn Township, Essex County, N.J., and Robert William Singleton, New York, N.Y., assignors to Celanese Corporation, a corporation of Delaware Continuation of application Ser. No. 321,994, Oct. 21, 1963, which is a division of application Ser. No. 70,509, Nov. 21, 1960. This application Dec. 22, 1966, Ser. No. 604,063

2 Claims. (Cl. 260-937) The present invention relates to the preparation of stereospecific polypropylene filamentary material.

This application is a continuation of application 321,- 994, filed Oct. 21, 1963, and now abandoned, which in turn is a divisional of application Ser. No. 70,509, filed Nov. 21, 1960 by Herman Dietrich Noether and Robert William Singleton.

Polyolefin filamentary materials have found limited application because of their pronounced tendency to extend excessively or creep upon prolonged application of loads even far below their breaking values. i

It is an object of the present invention to produce polypropylene filamentary materials exhibiting high tenacity, substantially no post yield ductility and substantially unchanged length even upon prolonged loading.

Other objects and advantages of the invention will become apparent from the following detailed description of the invention wherein all parts are by weight unless otherwise expressed.

In accordance with one aspect of the invention stereospecific polypropylene is dissolved in a volatile solvent and the solution is extruded through a plurality of orifices into an evaporative atmosphere to produce a plurality of filaments. The filaments are collected and the resulting bundle, e.g. a yarn, is taken up at a linear speed faster than that at which the solution left the orifices, i.e. the filaments are drawn down or stretched. This yarn is then subjected to second and third drawings. The second drawing is carried out at a fiber temperature of about room temperature to 110 C. at a draw ratio of about 2:1 to 10:1 and preferably at a fiber temperature of about to C. at a draw ratio of about 4:1 to 8:1, the tenacity being raised thereby to in excess of about 5 grams per denier. The third drawing is carried out at a fiber temperature of about to 150 C. at a draw ratio of about 1.1:1 to 4:1 and preferably at a fiber temperature of about 147 C. at a draw ratio of about 1.8:1 to 3.521. Advantageously the total draw ratio in the second and third drawings is at least about 9:1 and preferably at least about 12:1, the tenacity being raised thereby to in excess of about 8 grams per denier while the elongation exceeds 10% and often 15%. The stress-strain behavior of the yarn shows substantially no post yield ductility, i.e. the stress-strain curve is a relatively straight line.

The drawing temperatures recited hereinabove have reference to the temperature of the filaments which will usually be lower than the temperature of the drawing apparatus. For example, if a filament is to be drawn at C. and the medium is hot air, it may be necessary to heat the air to 150 to C. for the filament to reach the desired temperature in the short time it traverses the hot air zone; conversely, if the air temperature is 145 C. the filament temperature may be lower.

The starting material in accordance with the present invention comprises stereospecific polypropylene such as is produced by polymerization in the presence of the usual type of heterogeneous catalyst such as titanium trior tetrachloride plus an aluminum alkyl or in the presence of chromium oxide-alumina-silica catalyst. Minor amounts 3,377,329 Patented Apr. 9, 1968 of copolymerizable monomers may also be present. The product, usually called isotactic polypropylene, has a density ranging from about 0.88 to 0.92 gram per cubic centimeter and a melting point exceeding C. Its inherent viscosity usually exceeds about 1.0 andgener'ally ranges from about 1.5 to 4.0 as determined in 'decalin at 135 "C.

The polymer can be converted into filamentary material by dry -spinning as described above or by wet or melt spinning, as well as by various combinations thereof. While the filamentary material is usually attenuated during production it may be pulled along at 'a speed equal to or only a fraction of the extrusion speed. It should, however, be prevented from uncontrolled contraction and shrinkage and such positive control constitutes the first drawing step. The filamentary material may constitute a monofilament or a bundle of filaments, 'e.g. a "bundle of relatively few filaments such as a yarn or of very many filaments such as a tow which is ultimately intended for conversion into staple fiber, or the like.

The second and third drawings may be carried out sequentially with the production of the starting yarn and/ or with one another. While hot fluids such as water or air may be employed to bring the yarn up to drawing temperatures, hot rolls, pins, shoes or plates may also be employed either by themselves or in conjunction with one another. I v

The invention will be further described with reference to the accompanying drawing wherein:

Curve A is the stress-strain curve for an isotactic 'pol'ypropylene which has been spun into yarn and then drawn;

"Curve B is the stress-strain curve resulting from further drawing of the yarn of Curve A; and

Curve C is the stress-strain curve'of a commercial polypropylene yarn.

From a comparison of Curves A and B it can be seen that the product of Curve B is far strongerthan that of Curve A. Curve B is far closer to a straight line than Curve A and it is free of a sharp knee, which is a graphic representation of the low post yield ductility of the novel product, i.e. it does not commence elongating rapidly once the load exceeds some special value. The commercial material represented by Curve C also has a low post yield ductility but its tenacity at break is less than half that of the novel product. From the similarity between Curve C and the initial portion of Curve A it appears that the product of Curve C is the same as that of Curve A except for some treatment which reduces its elongation without improving its tenacity.

The post yield ductility can be evaluated by comparing the actual elongation at break tenacity with the elongation in excess of that obtained by extending the straight line portion of the stress-strain curve (Curve B) to the break tenacity (Curve B), i.e., the ratio of YX to ZX. With the novel products of this invention the ratio is less than about 0.7 and is often less than 0.6.

The novel product resulting from the three stage drawing exhibits an X-ray diagram the sharpness of which is equal to or greater than that of a product only twice drawn. However, its overall birefringence as measured by the Becke line method is about 0.035 or higher as contrasted with about 0.032 for the same material drawn but twice.

The thrice-drawn products are also characterized by marked stability or resistance to creep under load, e.g. under a load of 2 grams per denier they are extended usually less than about 6% even after 1200 hours. For the same length of time 3 grams per denier extend the fiber usually less than about 8% and 4 grams per denier less than about 10%. At a load of 7 grams per denier, which would break twice drawn material, the novel prod- (a) Commercial isotactic polypropylene having an inherent viscosity of 2.5, as measured in Decalin at 135 C., and a melting point of 168 C. is dissolved to a concentration of 24% in xylene. The solution is extruded through 5 circular orifices each 0.076 mm. in diameter into hot air at 100 C. The resulting filaments are pulled by a first pair of draw rolls driven at a peripheral speed of meters per minute and wound onto a bobbin with 0.3 turn per inch. The 98 denier product has a tenacity of about 1.5 grams per denier and an elongation of about 500%; the large variability between successive samples makes a precise determination impossible.

(b) The bobbin is removed, the yarn is advanced over a pin immersed in water at 93 C. onto a draw roll oper ating at a peripheral speed such that the yarn is drawn to 6.6 times its length and the yarn is collected on bobbins.

It has a tenacity of 6.03 grams per denier and an elongation of 37.7%, its stress-strain curve being shown in the drawing as Curve A. Under a constant load of 2 grams per denier in 1,000 hours the yarn is extended'55% and in 1500 hours it breaks at an extension of Under a constant load of 4 grams per denier the yarn breaks in 2 minutes.

(c) The yarn drawn as in (b) is then redrawn over a hot shoe 30 centimeters long and maintained at a temperature of 146-148 C. as measured by a thermocouple placed under the shoe surface. The yarn is fed to the shoe at 1.4 meters per minute and is drawn away from the shoe at 3.4 meters per minute, i.e. a draw ratio of 2.4:1. The yarn has a denier of 5.9, a tenacity of 10.4 grams per denier, an elongation of 13.7% and a post yield ductility of about 0.56. Its stress-strain diagram is shown in the drawing as Curve B. Under a constant load of 2 grams per denier in 1200 hours the yarn is extended 4%. Under a constant load of 4 grams per denier the yarn does not break even after 1,200 hours at which time it has extended 8%. Under a constant load of 7 grams per denier the yarn does not break even in hours, at which time it has extended 14%.

It is to be understood that the foregoing detailed de scription is given merely by way of illustration and that many variations may be made therein Without departing from the spirit of our invention.

Having described our invention what we desire to secure by Letters Patent is:

1. Creep-resistant stereospecific polypropylene filamentary material exhibiting a tenacity in excess of about 8 grams per denier, an elongation in excess of about 10%, and a post yield ductility of less than about 0.7, said filamentary material having been produced by extruding stereospecific polypropylene in liquid state through an orifice to produce a filament, drawing said filament continuously from said orifice, drawing said filament a second time at a temperature of about room temperature to C. and a draw ratio ranging from about 2:1 to 10:1, and drawing said filament a third time at a temperature of about to C. and a draw ratio ranging from about 1.1:1 to 4:1.

2. The filamentary material of claim 1 having a tenacity of 8 to 10.4 grams per denier, an elongation of about 10 to 13.7%, a post yield ductility of about 0.56 to 0.7, an extension of about 4 to 6% under a load of 2 grams per denier for 1200 hours, an extension of about 8 to 10% under a load of 4 grams per denier for 1200 hours, and an extension of about 14 to 20% at a load of 7 grams per denier for 100 hours.

References Cited UNITED STATES PATENTS 3,013,003 12/1961 Maragliano 26093.7 3,048,467 8/1962 Roberts et a1. 2642l0 JOSEPH L. SCHOFER, Primary Examiner.

LAWRENCE EDELMAN, Assistant Examiner. 

1. CREEP-RESISTANT STEREOSPECIFIC POLYPROPYLENE FILAMENTARY MATERIAL EXHIBITING A TENACITY IN EXCESS OF ABOUT 8 GRAMS PER DENIER, AN ELONGATION IN EXCESS OF ABOUT 10%, AND A POST YIELD DUCTILITY OF LESS THAN ABOUT 0.7, SAID FILAMENTARY MATERIAL HAVING BEEN PRODUCED BY EXTRUDING STEREOSPECIFIC POLYPROPYLENE IN LIQUID STATE THROUGH AN ORIFICE TO PRODUCE A FILAMENT, DRAWING SAID FILAMENT CONTINUOUSLY FROM SAID ORIFICE, DRAWING SAID FILAMENT A SECOND TIME AT A TEMPERATURE OF ABOUT TEMPERATURE TO 110*C. AND A DRAW RATIO RANGING FROM ABOUT 2:1 TO 10:1, AND DRAWING SAID FILAMENT A THIRD TIME AT A TEMPERATURE OF ABOUT 140 TO 150*C. AND A DRAW RATIO RANGING FROM ABOUT 1.1:1 TO 4:1. 